Insulating material for vacuum insulating system



Jan. 25, 1966 F. M. SIGONA 3,231,125

INSULATING MATERIAL FOR VACUUM INSULATING SYSTEM Filed Aug. 30, 1962 INVENTOR. FRANK M. SIGONA ATTORNEY 3,231,125 Patented Jan. 25, 1966 United States Patent Ofiice 3,231,125 INSULATING MATERIAL FOR VACUUM INSULATING SYSTEM Frank M. Sigona, Glendora, Calif., assignor to Aerojet- General Corporation, Aznsa, Califi, a corporation of Ohio Filed Aug. 30, 1962, Ser. No. 220,365

Claims. (Cl. 220-9) This invention relates to an insulating material and more particularly to an improved insulating material for use in a vacuum insulating system.

Recent improvements in the design of Dewar-type containers for holding or storing material at very low or at high temperatures has involved filling the otherwise evacuated insulating space between the double walls of the Dewar-type container with alternate layers of fiber and aluminum or metal foil. The aluminum or metal foil acts as a radiation-barrier or shield to prevent radiation of heat into or out of the container. The fibrous material which is a poor conductor of heat functions as a support for holding the sheets of aluminum or metal foil in spaced relation to each other between the double walls.

It has been found, contrary to expectation, that the transmission of the 'heat across such a solid in vacuumtype insulation is substantially reduced in comparison to the transmission of heat across a completely evacuated space. The insulating material heretofore used to fill the space between the double walls of the Dewar-type container is, as described in US. Patent 3,007,596, alternate layers of glass wool or fiberglass with aluminum or metal foil.

There were, however, a number of disadvantages to the insulating materials heretofore used. For one thing, these materials were quite expensive and they were difficult to handle. In addition, the insulating material could not easily be fitted into irregular spaces. Furthermore, the geometry or the spacing between the heat reflective sheets could not be maintained completely uniform. This factor was particularly important when the available evacuated space was quite small. Additionally, for certain applications as in association with an optical device, the use of the glass wool or fiberglass sheets were objectionable because the fiberglass or the glass wool has a tendency to break off and form lint which could interfere with the optical system.

A further disadvantage of the prior insulation material was that the use of the aluminum or metal foil between the fiber layers introduced material which is a good conductor of heat. Although the thickness of the individual sheets of aluminum or metal foil may be small, the insulation could have as many as 200 layers of foil per inch, so that the composite thickness of the aluminum or metal foil becomes an important and adverse factor in the conductivity of heat from or to the container.

What is needed, therefore, and comprises a principal object of this invention, is to provide an insulating material which is both more eflicient and easier to handle than the insulating material heretofore in use.

A further object of this invention is to provide an insulating material for a container comprising alternate layers of material which have a consistent geometry.

Yet another object of this invention is to provide an insulating material which does not shed or form lint.

This invention, in its broadest aspect, comprises forming an insulating material from. alternate layers of aluminized Mylar and silk. This material is preferably inserted between the double walls of a Dewar-ty pe container. This region is then completely evacuated to form a high efficiency multi-layer insulation for the container. Aluminized Mylar as used herein refers to a plastic film comprising a polyester of ethylene glycol and terephthalic acid on which a coating or layer of aluminum has been deposited.

This and other objects of this invention will become more apparent when understood in the light of the accompanying specification and drawings wherein:

FIGURE 1 is a front sectional view of a double-walled Dewar-type contain-er embodying the principles of this invention;

FIGURE 2 is a sectional View taken on the line 22 of FIGURE 1.

FIGURE 3 is an enlarged detailed sectional view showing the arrangement of the silk and aluminized Mylar which form a part of the insulating material; and

FIGURE 4 is an isometric view of the composite insulating material with parts broken away to show the underlying layers. Referring now to FIGURE 1 of the drawing, a Dewartype container indicated generally by the reference numeral 10 comprises an inner wall 12 and an outer wall 14. These walls are in spaced relationship to each other defining a region or space 16 therebetween. An outlet conduit 18 is connected to space 16 for reasons to become apparent below. Conduit 18 is connected to a valve 20 designed to seal off or open the conduit 18 communicating with space 16. With this arrangement, gas in space 16 can be evacuated by means of a suitable vacuum pump.

The interior 22 of the container is adapted to be filled with a material such as a cryogenic fluid. In the particular embodiment shown, the container may have an inlet and outlet conduit 24 and 26 respectively. An inlet valve 28 is mounted in inlet conduit 24 and anoutlet valve 30 may be mounted in the outlet conduit 26. In this way, the interior 22 of the container 10 may be readily filled with a cryogenic liquid through inlet conduit 24 and inlet valve 28, and the container may be evacuated to a pressure 10 mm. Hg or lower through the outlet conduit 26 and the outlet valve 30.

The space 16 between the inner wall 12 and outer wall 14- of container 10 is completely filled with an insulation material indicated generally by the reference numeral 32 (see FIGURE 2). This insulation material consists of alternate layers of silk 34 and aluminized Mylar 36 (see FIGURES 3 and 4). It has been found that a highly effective insulation material is provided by making the silk layers about 0.0015 inch thick and the layers of aluminized Mylar about 0.0005 inch thick which includes an aluminum coating on one side of the Mylar fillm of about 250 A. thick or 2.5 l0 mm. thick.

With this arrangement, the aluminized Mylar functions to reduce the radiant heat transfer to or from the interior 22 of the container while the layers of silk offer high resistance to heat conduction. The heat reflective characteristics of the aluminized Mylar does not depend upon its thickness; hence the superiority of aluminized Mylar in comparison to the thinnest available metal foil is apparent from the fact that the thinnest feasible aluminum foil is approximately 2 10 mm. thick, while the layer of aluminum deposited on the Mylar is of the order of 2 10 mm. thick. As a consequence, there is less heat conductive material in the insulation so that the above-described insulation between the double walls of the container 10 produces a decrease in heat transfer of from 25 to times that obtained witha pure vacuum, and an improvement factor of 10 to 60 times in heat transfer in comparison to a conventional vacuum plus the prior powder insulation previously used. It has been found that the coefiicient of t-herrno conductivity for the above-described insulation is approximately 0.7 microwatt per centimeter per degree centrigrade. As

3 a result, the above-described insulation is superior in performance, and from the point of view of handling ease and utility, to the insulation material previously available.

It is to be understood that the form of the invention herewith shown and described is to be taken as a preferred example of the same, and that various changes in the shape, size, and arrangement of the parts may be resorted to without departing from the spirit of this invention or the scope of the claims.

I claim:

1. An apparatus of the class described comprising a container, said container having a double wall, an insulating material in said double wall, said insulating material comprising alternate layers of silk and a polyethylene terephthalic film having a coating of aluminum thereon, and means for evacuating said space between the double walls, whereby the heat transmisison through the double walls is substantially decreased.

2. An apparatus of the class described comprising a container, said container having an inner wall and an outer wall, and defining thereby an insulating space surrounding the container, an insulating material mounted in said insulating space, said insulating material compris ing a plurality of alternate layers of silk and a polyethylene terephthalic film having a coating of aluminum thereon, and means for removing gas in said insulating space at a pressure at least 10 mm. of Hg, whereby the heat transmission across said space is substantially decreased.

3. An apparatus of the class described comprising a container, said container having an inner wall and an outer wall, and defining thereby an insulating space therebetween, an insulating material mounted in said insulaming space, said insulating material comprising a series of alternate layers of silk and a polyethylene terephthalic film having a coating of aluminum thereon,

said silk being about .0015 of an inch thick and said polyethylene terephthalic film having the coating of aluminum thereon being about .0005 of an inch thick including an aluminum coating on one side of about 250 A. thick, and means for evacuating gas from said insulating space whereby the heat transmission through said insulating space is decreased by the radiant heat barrier formed from said layers of polyethylene terephthalic film having the aluminum coating thereon while heat conduction through said insulating space is resisted by said layers of silk.

4. An insulating material of the class described, said insulating material comprising alternate layers of silk with a polyethylene terephth'alic film having a. coating of aluminum thereon, said polyethylene terephth'alic film having the coating of aluminum thereon being about .0005 of an inch thick including an aluminum coating on one side of about 250 A. thick.

5. An insulating material of the class described comprising alternate layers of a polyethylene terephthalic film having a coating of aluminum thereon and silk, said silk being about .0015 of an inch thick, said polyethylene terephthalic film ha ving the coating ;of aluminum thereon being about .0005 of an inch thick With the aluminum coating on one side of about 250 A. thick.

References Cited by the Examiner UNITED STATES PATENTS 2,703,772 3/1955 K eithly l54--46 2,863,179 12/1958 Gaugler 154-45 3,009,600 11/1961 Matsch 2209 3,039,904 6/1962 Stage 154-'46 3,059,364 10/1962 Landsberg et al. 154-44 THERON E. CONDON, Primary Examiner. EARLE J. DRUMMOND, Examiner. 

1. AN APPARATUS OF THE CLASS DESCRIBED COMPRISING A CONTAINER, SAID CONTAINER HAVING A DOUBLE WALL, AN INSULATING MATERIAL IN SAID DOUBLE WALL, SAID INSULATING MATERIAL COMPRISING ALTERNATE LAYERS OF SILK AND A POLYETHYLENE TEREPHTHALIC FILM HAVING A COATING OF ALUMINUM THEREON, AND MEANS FOR EVACUATING SAID SPACE BETWEEN THE DOUBLE WALLS, WHEREBY THE HEAT TRANSMISSION THROUGH THE DOUBLE WALLS IS SUBSTANTIALLY DECREASED. 